The 106-RPS-RR and 206-RPS-RR surge anticipating relief on rate of rise valves are based on the 106-PG or 206-PG main valve.
The valve is installed downstream of the pump check valve(s) and has two pilots, the 81-RP and the 81-RPD. Both pilots sense pressure through a connection to the header pipe. The 81-RP high pressure pilot acts as a standard relief pilot, opening on excessive pressure. The 81-RPD differential pilot responds to the pressure differential across its diaphragm. A pressure differential is created when there is a system pressure increase. The flow into the accumulator creates a pressure drop across the fixed restriction, which lowers the pressure in the connection between the fixed restriction and the pilot.
The pilot senses the pressure difference between this lower pressure and the header pressure. This difference occurs at the initiation of the pressure surge, providing the time necessary for the valve to open in anticipation of the high pressure.